1. Field of the Invention
The present invention relates to a display unit. It more particularly relates to the field of electric, light signs and markings. For the latter, use has hitherto been made of photoemissive diodes or lamps.
2. Discussion of the Background
It has been forbidden to use lasers, which emit coherent electromagnetic rays, which can give rise to serious injuries to the eyes of observers.
In order to provide protection against the lasers, it is known to use materials able to absorb laser beams, but if in this way users are protected, they are inter alia also deprived of visible information concerning the presence of laser beams.
In order to reveal the presence of a laser beam, use is presently made of complex and costly means requiring electric power to operate. Such means consist e.g. of pilot lamps, photodetectors, electronic cameras and means for measuring power by absorption by a black body.